The present invention relate to a process for the preparation of polybutylene terephthalate (PBT) based polymer by using a complex catalyst which consists of titanium compounds and antimony compounds.
More particularly, the present invention relates to a novel and improved preparation method of PBT, which includes a polymerizing step using a complex catalyst composed of either one or both of titanium compounds of general formula (I) and general formula (II), and antimony compounds. ##STR1## wherein R and R' represent individually, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, acetylisopropyl, pentyl, hexyl, heptyl, 2-ethyl hexyl, octyl, decyl dodecyl, tridecyl, octadecyl, stearyl, allyl, 2,2-diallyloxymethylbutyl, cyclopentyl, cyclohexyl, naphthyl, phenyl, benzyl or dodecyl benzyl group.
Antimony compounds can be selected from the group consisting of antimony trioxide, antimony triacetate or antimony ethyleneglycoxide.
Common PBT manufacture has been widely used in films and plastic mouldings industrial due to its excellent physical properties such as moulding, heat-resistance and chemical-resistance. Generally, the process of this invention (PBT) comprises a direct esterification step or an ester interchange step of terephthalic acid or dimethyl terephthalate with 1,4-butanediol (hereinafter, BD), forming bis(.delta.-hydroxy butyl) terephthalate and/or its oligomer thereof (hereinafter, ester compound) and a condensation step of produced ester compound under the reduced pressure, thereby obtaining the higher polymer.
In the above mentioned esterification (direct esterification or ester interchange) and condensation, reaction catalyst which is composed essentially of metal catalyst such as titanium and antimony compound, is required to increase the velocity of the reaction.
It is well-known that color and physical properties of produced polymer as well as the velocity of reaction depend on the type and the amount of used catalyst.
The higher polymer (PBT) preparation method using titanium catalyst exhibits a fast rate of reaction. However, it involves problems such as coloration of the resultant polymer and excessive production of side-product, tetrahydrofuran (Japanese patent laid-open publication No. 48-47594, Patent Publication Nos. 55-34829 and 55-30010). Also, titanium compounds are good as reaction catalyst, but have defects that they are hydrolyzed easily with water produced during the reaction to form insoluble impurities and their catalytic activity has been declining sharply.
Thus, to solve the problems mentioned above, the process of adding catalyst divided before and after esterification (Japanese patent laid-open publication No. 49-57092), and the process of adding Iodine compound before condensation (Japanese patent publication Nos. 55-7853 and 63-40209), are known but they have a limited effect.